1. Technical Field
The present invention relates to a piezoelectric device and a piezoelectric device manufacturing method.
2. Related Art
Currently, a crystal oscillator is often included in an electronic apparatus such as a cellular phone. The crystal oscillator has a crystal oscillating piece sealed into a package. For manufacturing the crystal oscillator, a method which includes steps of forming an oscillator substrate containing the crystal oscillating piece and an outer frame surrounding the crystal oscillating piece as one piece body, and joining sealing substrates to both surfaces of the oscillator substrate has been proposed (for example, see JP-A-2007-258918 (Patent Document 1) and JP-A-2008-271491 (Patent Document 2)).
According to the methods disclosed in Patent Documents 1 and 2, the crystal oscillating piece is formed on each of a plurality of areas of an intermediate crystal wafer, and then a sealing crystal wafer is joined to each of the upper and lower sides of the intermediate crystal wafer. Subsequently, the plural areas are divided into individual pieces with the areas of the intermediate crystal wafer around the respective crystal oscillating pieces provided as the external frames to manufacture the plural crystal oscillators at a time. According to this method, the productivity considerably increases compared with that of a method which mounts the crystal oscillating pieces by steps separated for each crystal oscillator.
According to the method shown in Patent Document 1, the intermediate crystal wafer and the sealing crystal wafers are joined to each other by surface-activating junction. According to the method shown in Patent Document 2, metal films for joining the intermediate crystal wafer and the sealing crystal wafers are formed. In this method, a metal paste sealing agent is applied between the metal films, and then is burned to join the intermediate crystal wafer and the sealing crystal wafers. When the wafers are connected almost without using organic solvent as in this method, deterioration of the crystal oscillating piece and lowering of oscillation characteristics caused by gas generated from the organic solvent can be reduced.
While high-quality crystal oscillators can be manufactured with high efficiency according to the technologies disclosed in Patent Documents 1 and 2, the following problems still remain as points to be improved.
According to the methods shown in Patent Documents 1 and 2, the intermediate crystal wafer is joined by surface-activating junction or metal junction. Thus, the intermediate crystal wafer containing the crystal oscillating pieces are rigidly fixed. In this case, an impact force given from the outside is easily transmitted to the crystal oscillating pieces, and thus the shock resistance of the crystal oscillators lowers. Moreover, the oscillation of the crystal oscillating pieces is easily diffused to the sealing crystal wafers, and thus the oscillation characteristics such as the Q factor lower in some cases.